The present invention relates to a high dimensional cored wire containing de-oxidant material (or oxygen remover). Furthermore the invention relates to a process for manufacturing a high dimensional cored wire.
De-oxidation plays an important role in the process of steel making, for which a number of deoxidants have been conventionally used. The term de-oxidant means a chemical compound, alloy or element which will remove the active oxygen present in the liquid metal (e.g., steel) and form an oxide as its final product, usually as a distinct phase and easily separable from the liquid metal. Oxygen, if present in steel in the active/elemental form, will result in pinholes and blowholes in the cast product as well as obstruct the process of continuously casting the steel in the modern continuous casting machines. Steel makers are in regular search of a better and more economical method for removing the oxygen in steel, which will ultimately reduce the consumption of deoxidants.
Conventionally, de-oxidation of steel was carried out by the addition of ferro alloys or aluminum ingots, bars or solid aluminum wire. For bars and ingots the recovery (i.e., ratio of actual quantity and theoretical amount of aluminum) was poor, resulting in greater aluminum consumption. In the case of aluminum wire, the recovery was better, but feeding time was greater, and often the wire could not reach the depth of the molten steel bath.
For doing the primary de-oxidation or the bulk removal of oxygen (primary killing) in steel from a higher level of, say, 800-2000 ppm and above, to a lower level of around 100-200 ppm, alloys such as “ferro-silicon,” “ferro-manganese,” “silico-manganese,” and “coke” are used, though in bulk, and these materials have served the purpose fairly well. These ferro alloys or compounds have a limitation on the extent to which they can be used in steel making and are limited to the extent of the specification that is allowed in the steel. In almost all grades of steel, silicon and manganese elements are used in various forms for the primary de-oxidation, along with aluminum in various forms such as bars, ingots, cubes or solid wires, etc.
For secondary treatment of steel for the purpose of removing the remnant of oxygen, a number of de-oxidants selected from the group of aluminum, titanium and calcium silicide have been used. However, aluminum has been found to be the most suitable de-oxidant for two reasons, e.g., (i) affinity of aluminum for active oxygen and (ii) the requirement of presence of aluminum in predetermined amounts in some grades of steel in the cast product. Aluminum is capable of removing oxygen present in molten steel at very low levels of around 4 ppm or even less. It is also the most economical de-oxidizer element, alloy or compound known at present.
Previously, primary de-oxidation, apart from the use of ferro alloys, was carried out by the addition of aluminum ingots or bars and solid wires of dimension of 13 mm, and secondary or final de-oxidation by adding ingots, notch bars and sometimes even solid aluminum wire. Addition through solid aluminum wire results in a higher percentage of recovery of aluminum compared to bars and ingots. In this specification, unless otherwise specified, the term ‘recovery’ defines the ratio of the actual quantity of aluminum to be added to remove the active oxygen to the theoretical amount of aluminum required. For bars and ingots, the recovery was very poor and accordingly consumption of aluminum increased. In the case of solid aluminum wire, though the recovery was better than bars and ingots, feeding time was greater. The normal size of the aluminum wire that can be injected into the molten steel is around 3 ,6, 9, 13, or 16 mm.
The other problem encountered with solid aluminum wire is that due to the high temperatures encountered in steel making, aluminum becomes very soft due to the high temperatures and is not able to penetrate deeply into the molten steel bath which consequently results in lower recovery.
To solve a similar problem, it is proposed in Chinese patent application publication CN 1498975 A to feed aluminum cored wire directly into molten steel for deoxidizing.
A further method of adding aluminum to steel in a ladle for the purpose of de-oxidation is known from British patent application publication GB 892375. This method comprises progressively feeding a rod or wire of the material to be added at an appreciable depth below the surface of the steel. The material may be in powder or granular form enclosed in a steel tube.
A process for manufacturing cored wires containing deoxidizing constituents as pulverized material within a metal tube is known from U.S. Pat. No. 3,915,693.